Adaptive output feedback control of nonlinear SISO systems via singular perturbation technique

The paper presents an approach to adaptive output feedback controller design for single-input-single-output (SISO) nonlinear systems based on the use of the singular perturbation technique. The presented approach guarantees desired output transient performance indices by inducing of two-time-scale motions in the closed-loop system. It has been shown that stability conditions imposed on the fast and slow modes and sufficiently large mode separation rate between fast and slow modes can ensure that the full-order closed-loop nonlinear system achieves the desired properties in such a way that the output transient performances are desired and insensitive to external disturbances and plant´s parameter variations. The high-frequency-gain online identification and adaptive gain tuning are incorporated in the control system in order to maintain the two-time-scale structure in the closed-loop system trajectories and stability of fast-motion transients for a large range of plant´s parameter variations. Numerical example and simulation results are presented.